1. Field of the Invention
The present invention relates generally to integrated circuit chip package technology and, more particularly, to a QFP semiconductor package which includes stacked semiconductor dies and exposed leads on the bottom of the package body thereof.
2. Description of the Related Art
Integrated circuit dies are conventionally enclosed in plastic packages that provide protection from hostile environments and enable electrical interconnection between the integrated circuit die and an underlying substrate such as a printed circuit board (PCB). The elements of such a package include a metal leadframe, an integrated circuit die, bonding material to attach the integrated circuit die to the leadframe, bond wires which electrically connect pads on the integrated circuit die to individual leads of the leadframe, and a hard plastic encapsulant material which covers the other components and forms the exterior package body of the semiconductor package.
The leadframe is the central supporting structure of such a package. A portion of the leadframe is internal to the package, i.e., completely surrounded by the package body. Portions of the leads of the leadframe extend externally from the package body of the package, or are partially exposed within the package body for use in electrically connecting the semiconductor package to another component. In certain semiconductor packages, a portion of the die pad of the leadframe also remains exposed within the package body for use as a heat sink.
One type of semiconductor package commonly known in the electronics field is referred to as a quad flat pack (QFP) package. A typical QFP package comprises a thin, generally square package body defining four peripheral sides of substantially equal length. Protruding from each of the four peripheral sides of the package body are a plurality of leads which each have a generally gull-wing configuration. Portions of the leads are internal to the package body, and are electrically connected to respective ones of the pads or terminals of a semiconductor die also encapsulated within the package body. The semiconductor die is itself mounted to a die pad of the QFP package leadframe. In certain types of QFP packages referred to as QFP exposed pad packages, one surface of the die pads is exposed within the bottom surface of the package body.
In the electronics industry and, in particular, in high frequency applications such as cell phones, PDA's, Bluetooth, and IMT2000, there is an increasing need for QFP exposed pad packages of increased functional capacity. The present invention provides such a QFP exposed pad package wherein stacked semiconductor dies are encapsulated by the package body and leads are exposed within the bottom surface of the package body. The semiconductor package of the present invention is provided through the use of standard, low-cost leadframe design techniques. These, as well as other features and attributes of the present invention, will be discussed in more detail below.